This invention relates to a three-phase magneto generator and more particularly to such a device that provides a greater and more uniform output for a given driving force and at a lower temperature to provide a more compact generator.
Conventional magneto generators have a rotor carrying permanent magnets that is driven by a prime mover such as an internal combustion engine to induce voltages in stator coils as the rotating magnetic fields pass the stator coils. The number of magnetic poles of the permanent magnets disposed in the rotating (circumferential) direction of the rotor is 2n where xe2x80x9cnxe2x80x9d is a positive integer. This is because the same number of N-poles and S-poles must be located at equal intervals in the circumferential direction. In the case of a three-phase generator, the number of teeth or armature cores P of the stator core is 3m with xe2x80x9cmxe2x80x9d being a positive integer.
Conventionally, n=m. That is, when the number of magnetic poles M of the rotor is arranged as 2n, the number of teeth P of the stator core is set to 3m=3n. For example, when n=6, the number of magnetic poles M is set to 12, the number of teeth or armature cores P is 18. When n=8, those numbers are defined as M=16, and P=24.
This conventional relationship is shown in FIGS. 1 and 2 that show respectively, a partial cross sectioned front view a diametrical cross section a magneto generator, with n=m =6, or M=12 and P=18. A rotor, shown generally at 21, comprises a boss portion 22 is driven for example by being secured to a crankshaft (not shown) of an internal combustion engine or other suitable prime mover. The rotor 21 further comprises a generally cup-shaped cup portion 23 secured to a flange of the boss portion 22. A plurality of annular permanent magnets 24 are suitably secured to the inside circumferential surface of the cup portion 23. The permanent magnets 24 are magnetized to have 2n poles of opposite polarities in the circumferential direction. This conventional example is arranged as n=6, and so number of magnetic poles M is 2n=12.
A stator 25 cooperates with the rotor 21. The stator 25 is comprised of a stator core formed by laminating thin steel plates having teeth or armatures 26 on which coils 27 are wound. The number of teeth 26 of the stator 25 is 18. In this case, m=6 because 3xc3x97m=18. The coils 27 have U-, V-, and W-phases. The coil of each phase is wound on every three teeth 26 in succession. In this case, the every three teeth or armature on which the coils 27 of the same phase are wound oppose the same polarity of the magnet 24 at the same electrical angle. In order to arrange that the teeth of the same phase oppose the same polarity of the magnet 24 at the same electrical angle as described, it is necessary that either n=m or at least n is an integer multiple of m.
With the conventional generator as described above, since electricity is generated in the state of that the m (six) teeth 26 wound on the coils 27 having same place are opposed to the m (six) permanent magnets in the same phase, harmonics induced at the respective m (six) teeth are superimposed in the same phase, and distortion in the output waveform is intensified. This distortion is graphically illustrated in FIG. 3. The three phase wiring diagram for the machine and voltage outputs V1 and V2 are shown in FIG. 4.
Because of this distortion the torque required for driving the rotor 21 increases for a given output to be produced. This problem has been exacerbated in recent years because the performance of permanent magnets has been significantly improved. For example, the neodymium-iron-boron magnet having a high maximum magnetic energy product has come to be known. When such a high performance magnet is used, variation in the driving torque for the rotor also increases.
With the increase in the driving torque, when the rotor is driven with an internal combustion engine, cyclic variation in the load on the engine also increases. This in particular necessitates increase the of the driving power or output of the engine. This is shown in the broken line curves of FIG. 5. In the case the generator is driven with the engine, this means that the size of the engine increases. Moreover, since the coils of respective phases are connected in series at the same electrical angle, generated voltage is increased, but the output voltage waveform is not smooth and includes many harmonics, resulting in a low generation efficiency as also shown in this figure.
This further results in problems of self-heat generation of the generator as seen in the broken line curve of FIG. 6. Thus the amount of generated electricity cannot be increased without increasing the size of the generator.
Moreover, the output voltage waveforms in respective phases are heavily disturbed and include many sharp spike-shaped waveforms with high peak voltages as seen in FIG. 3. This has necessitated a capacitor for smoothing the output voltage which, in turn, has resulted in the use of a large size and high cost capacitor. Such problems become particularly acute when the neodymium-iron-boron magnet is used.
It is therefore an object of this invention to provide a three-phase magnetic generator that makes it possible to reduce the size and power of the driving prime mover by reducing the driving torque while at the same time improving the generation efficiency by smoothing the output voltage waveform.
It is a further object of the invention to reduce the size of coils or to produce a high output by making the coils compact by reducing the amount of self-generated electricity and also to reduce the size and cost of the smoothing capacitor by reducing the peak voltage or totally eliminating the need for such capacitors.
This invention is adapted to be embodied in a generator that is comprised of relatively rotatably first and second components. The first component has affixed to it in circumferentially spaced array, a plurality of segmented cylindrical, permanent magnets. The second member has a plurality of armature teeth around which coils are wound so that an electrical current will be induced in the coil windings upon relative rotation between the two members. The configuration is such that no more than two armature teeth are in registry with a single magnetic segment during the relative rotation.
In accordance with another feature of the invention, the configuration is such that the voltages induced at the armature teeth is the same phase voltage and of the same phase around the circumference of the machine.
In accordance with a still further feature of the invention, this is achieved by having the number of magnetic poles being equal to 2n and the number of armature teeth is equal to 3m where n and m are positive integers and that 2n divided by m is not an integer.